More than 500 million fluorescent lamps are produced and discarded every year in the United States alone, in Germany, some 90 million. Worldwide, the total number of fluorescent lamps themselves produced and discarded is estimated to be over a billion. A typical four-foot (1.2-m) fluorescent lamp may be made to contain about from 150 to 450 mg of mercury. In addition, a staggering amount of household batteries are produced and discarded, several billion yearly in the U.S. alone. Such products contain a wide variety of heavy metallic elements and compounds which end up in landfills. Leaching by rainwater slowly spreads heavy metallic leachates into groundwater, from which about half of the U.S. population obtains drinking water.
Of the heavy metals, mercury is especially undesirable in water because of its known toxicity, as evidenced by the advisories widely disseminated against eating fish caught in lakes, rivers, etc., due to mercury contamination. Mercury is also unique in being volatile as a metal, which is taken advantage of in fluorescent lamps. By-products of mercury in these lamps include mercury oxides, which are slowly leachable into groundwater. Because of their energy efficiency, fluorescent lamps are replacing other lights dramatically, thus increasing environmental concerns for the presence of mercury. Thus, laws declaring fluorescent lamps a hazardous waste are being enacted.
Mercury sulfides can form in soils under reducing or anaerobic conditions. In sludge, landfills, and in muck in lakes and rivers, mercury is chemically reduced by action of bacteria to methyl mercury. The latter is many times more volatile than mercury itself and engenders a much more rapid dissemination of mercury into the environment and biosphere.
Other dangerous heavy metals such as arsenic can also be reduced under anaerobic conditions to a hydride. Antimony behaves similarly. These hydrides can become problematical.
Cadmium is a carcinogen.
As well, huge, contaminated plant sites with sediment regions exist and in the U.S. are part of "Superfund" sites. Such sites, when contaminated with mercury, may be a result, for example, of chlor-alkali production plants which employed liquid mercury in their electrolytic processing. Wastewater and soil which originally had only mercury metal now has methyl mercury and various mercuric oxides as well.
Various procedures to remove metals such as mercury are known. However, these procedures are expensive to carry out and/or only partially effective, especially, for example, in removal and disposal of mercury values of fluorescent lamps.
One method of attempting to dispose of the "special waste" mercury of fluorescent lamps, practiced in Germany, employs a crushing step, followed by the addition of sulfur or zinc, which chemically bonds mercury vapor into mercuric sulfide and zinc alloy. The immobilization of the mercury is only partially effective.
Incinerators of household waste produce dust containing mercury.
Electrostatic dust precipitators do not collect mercury, but carbon filters can. By employing carbon filters, for example, one Berlin combustion/incineration facility meets emission standards for mercury. However, this method is expensive and is not of direct or wide applicability.
The German Osram process to dispose of mercury in fluorescent lamps entails removal of the aluminum ends of the lamps, blowing out the internal lamp powder (calcium chloro fluoro phosphate enriched with heavy metals including mercury) to provide "special waste" for subsequent disposal. The glass tubing is considered non-hazardous. However, this process does make a special hazardous waste, although of a much smaller volume than the original lamps.
The German MRT process entails removal of fluorescent lamp ends, blowing out the powder and heating of the powder to distill out metallic mercury. The glass tubing is considered non-hazardous. This process does not remove heavy metal values other than those found as metallic mercury, leaving behind mercuric oxides, and other heavy metal values.
The Herborn process, practiced in Germany and Austria, can employ a mobile apparatus. It entails shredding the fluorescent lamps, heating to distill out metallic mercury, and trapping of the mercury vapor in activated carbon. It also does not remove heavy metal values other than from metallic mercury, and it is expensive to carry out.
The aqua-control process, practiced by the Berlin Sanitation Department, entails crushing the fluorescent lamps and slurrying the crushed lamps in a sulfide solution to immobilize heavy metals as oxides and sulfides. A black sludge is obtained as "special waste" for further disposal. This process is also expensive and inefficient.
Thus, no known process is fully acceptable commercially.
Even so, the reduction of heavy metals in waste streams remains of great concern. See e.g., Report of the National Technical Forum on Source Reduction of Heavy Metals in Municipal Solid Waste, U.S. Environmental Protection Agency, EPA 901-R-93-001, September 1993; Hansen & Fisher, "Elemental Distribution in Coal Fly Ash Particles," Environmental Science & Technology, 14(9):1111-7, September 1980.
Among patent references, a Feb. 7, 1933 U.S. Pat. No. 1,896,876, to Wildman, discloses a process of recovering mercury by dissolution of a water insoluble mercuric sulfide by exposing the mercuric sulfide to an aqueous solution of sodium sulfide, which dissolves it as a double salt complex containing sodium and mercury. Next, after filtration, sulfur dioxide is passed into the solution, which decomposes the complex and again precipitates mercuric sulfide. Mercury can be thus separated from admixtures with other metals. This patent is aimed at recovering mercury from ores such as cinnabar but generally is not useful for other heavy metals. It is a "wet" method.
Ashley et al., U.S. Pat. No. 2,846,305 (Aug. 5, 1958), discloses a separation and recovery of mercury by treating sludges containing colloidal mercury and alumina with sulfuric acid generally of a 10-80 percent concentration. This dissolves the alumina selectively but does not convert mercury metal to mercury sulfate. It, too, is a "wet" method.
Ball et al., U.S. Pat. No. 5,013,358 (May 7, 1991), discloses a method for the recovery of mercury from mercury-containing material by using chlorine gas, which converts metallic mercury and water insoluble mercury salts, especially mercurous chloride (calomel), to mercuric chloride, as by an oxidation reaction, and thereby makes the mercury values soluble in water. Chlorine gas, however, has difficulties of its own, not the least of which concern its handling. It employs a chlorination method.
It would be desirable to provide a new way in which such metal values could be inexpensively and readily removed. A new way such as this would be most desirably useful to help remove heavy metal, e.g., Hg, values from fluorescent lamps.